(a) Field
The subject matter disclosed generally relates to media signal labeling. More specifically, it relates to the generation of time-related labels for media signals.
(b) Related Prior Art
Television in North America and some other regions of the world is typically generated with a video frame rate of 30/1.001 frames per second. As a result the number of video frames in a 24 hour period is not an integer value and also the phase alignment of the video frame boundaries to the 24 hour midnight rollover varies from day to day. For television production and broadcast applications, it is desirable and required to have the media frames labeled so that the video and its related audio signals may be controlled accurately and efficiently. Precise timing is critical for synchronization and seamless broadcast presentation. A labeling standard commonly referred to as “SMPTE time code” was developed by the Society of Motion Picture and Television Engineers (SMPTE) to label each video image frame with a time code number. For user utility and convenience, this label includes a time address number in the form of hours (00 to 23), minutes (00 to 59), seconds (00 to 59), and frames (00 to 29). With this labeling applied to video frames at a rate of 30/1.001 Hz, there is a drift of the time code and time address value as compared to a wall clock. To alleviate this drift, there is a modified counting mode referred to as 30 drop frame that modifies the count sequence to compensate for most of this drift (but not the whole drift). When this time code is required to maintain a more precise relationship to clock time, a daily correction is required. This daily correction is commonly referred to as a daily jam. This process of a daily jam is currently non-deterministic and is not standardized (since it can be implemented in various ways which may not be consistent). With the advent of packet switched technologies such as Ethernet and packetized media for television systems, there is a need to develop new techniques for controlling and synchronizing video and audio signals in a television system.
There exists methods and systems that are used to time code media samples. The methods try to associate a true time to media samples whose time codes contain an amount of drift which can arise from having non-integer frame rates. Adjustments with offset parameters are made to adjust the time coordinates.
There is thus a need for a method to determine the label of a media frame using deterministic and reversible calculations. There is a need for a system that would be fully deterministic so that it would be possible to convert from a point in time on one timescale to a corresponding point on another scale and to then convert back to the original time point. For example, a clock time could be converted to a frame label and then independently back to a clock time.
There is further a need to better account for leap seconds and days (on leap years), for changes between daylight saving time and standard time and for global synchronization between media.